1. Field of the Invention
The present invention relates to devices used for the directing the flow of fluids. More particularly, the present invention relates to devices for rapidly switching the direction of flow of fluids, including, but not limited to, those gases associated with the incineration of volatile organic compounds. Still more particularly, the present invention relates to valving used in multi-port fluid transfer system. The present invention is a diverting damper.
2. Description of the Prior Art
One method used to reduce the emission of hazardous fluids, including organic gases created through the production of a wide variety of organic compounds, is regenerative incineration. Regenerative incineration involves the oxidation of hazardous fluids. That is, organic compounds are reduced to relatively inert and relatively harmless gases through combustion. However, many organic compounds require extremely high temperatures--on the order of 600.degree. F. or more--for combustion to take place. A tremendous amount of energy is needed to establish and maintain the high temperatures necessary to ensure substantially complete combustion, as that term is understood in the governing environmental regulations. Further, given the spatial variation in temperature that can easily occur in a combustion chamber, there is no a priori certainty that such regulations will be met simply by raising the apparent temperature of the combustion chamber above the threshold.
In order to create more certainty in the combustion process, and in order to achieve substantially complete combustion within a combustion chamber while also reducing the expenditure of energy, it is a common practice in the field of hazardous fluid removal to add a catalyst to the combustion chamber. The catalyst aids in the reaction process used to create the products of combustion. The catalyst, which may be a plurality of suitable catalysts--or simply an inert material designed to increase dwell time within the chamber--thereby enables substantially complete combustion at a much lower processing temperature.
A generic hazardous-fluids combustion system is illustrated in FIG. 1. As shown, a combustion chamber 10 includes two reaction beds 11 and 12 in communication with one another and having reaction bed ports 13 and 14, respectively. However, it is to be noted that the combustion chamber 10 may have some number of reaction beds other than two. The combustion chamber 10 includes one or more catalysts, usually in each reaction bed. Incoming hazardous fluid enters a multi-port valve 15 from an upstream production unit, by way of a process fluid port 16. The multi-port valve 15 is designed to transfer the hazardous fluid from the fluid port 16 to the combustion chamber 10 that includes reaction beds 11 and 12. After sufficient dwell time in the combustion chamber 10, the combustion products are transferred to an exhaust stack 17 via stack port 18. The valve 15 includes reaction valve ports 19 and 20 for receiving reaction products from the chamber 10, or for delivering non-, or partially-reacted hazardous fluids from beds 11 and 12, respectively. Additionally, the valve 15 may include purge ports 21 and 22 for the introduction and removal of purge air to and from the valve 15.
It is important to note that while the catalyst aids in the oxidation of the hazardous fluid, the enhanced reaction that it produces within the chamber 10 is non-uniform. That is, the reaction occurs over a period of time such that when the hazardous fluid first enters the chamber 10 at a particular temperature--say for example with the fluid moving from valve 15 to reaction port 13--the reaction begins to take place, assuming the temperature at that location is sufficient to initiate the reaction. It accelerates as the heated fluid passes through the chamber 10. As a result, when the fluid moves from bed 11 to bed 12, the temperature within that zone including bed 12 increases to the point that it is greatest at reaction port 14. Correspondingly, the temperature of the fluid at reaction port 13 is lowest within the chamber 10. Through this process, the catalytic capacity of the catalyst is exhausted non-uniformly, with more catalyst available for the reaction near port 13 and less available near port 14. More importantly, the reacted fluid moving from port 14 through valve 15 to stack 17 is at a higher temperature than is the unreacted fluid at port 13. This is a waste of energy directly up the stack 17.
In the field of hazardous fluids combustion, the uneven use of the catalyst in chamber 10, and the waste of energy caused by exhausting higher temperature fluid to stack 17, has been reduced through the design of valve 15. Specifically, the valve 15 is preferably a switchable one that enables the rapid and certain reversal of fluid flow within the system. The switching is designed to direct the hazardous fluid to the higher-temperature end of the combustion chamber and to exhaust the chamber from its lower-temperature end. Preferably, this switching occurs fairly often--generally on the order of every five minutes or less. In this way, no one side of the chamber gets too hot and the loss of energy by way of the exhaust stack is minimized. Also, no one portion of the catalyst is compromised, or otherwise made less effective, sooner than any other portion. As a result of this technique, the system is deemed to be "regenerative." i.e., the heat of the process is used to drive the process.
Prior-art designs of the valve 15 achieve fluid switching with variable levels of success. The most common design includes multiple valving units forming the valve 15. These multiple units include extensive ducting, and they require substantial control means in order to ensure necessary synchronization. Failure to ensure that no hazardous fluid flows directly from port 16 to stack 17 will result in the exhausting of the hazardous fluid directly to the atmosphere--an unacceptable outcome. Unfortunately, the prior-art devices are complex and expensive. For the most part, they include one butterfly valve for each port, and they require extra piping in order to complete the fluid transfer. Thus, for a relatively simple system including four ports, four valves are required. This necessarily results in significant expense in the original fabrication of the valve unit, as well as in its maintenance. Moreover, the additional piping results in the retention of untreated fluid when the valving is actuated and fluid diversion occurs. The retained fluid is then diverted, untreated, directly to the exhaust. Further, the pressure drops associated with the switching of the fluid are undesirable, particularly during the crossing-over of the fluid from one port to another. Coordinated control of the valving is particularly important.
Poppet valves are also used as fluid diversion devices; however, given the fluid volumes and flow rates ordinarily experienced in this field, the pressure drops resulting from the use of such valves are too great to make them practical. Specifically, the poppet is oriented at an angle of approximately 90.degree. to the flow of the fluid. When the poppet valve is actuated, the fluid flow is diverted by that much, and the labyrinthine interiors of those valves result in considerable pressure drops.
One prior-art switching valve has been described in detail in U.S. Pat. No. 5,375,622 issued to Houston. The Houston device is a rotary valve for regenerative incinerators. However, there are several concerns associated with the design of the Houston valve. First, it is apparent that that device must overcome significant gas pressures in order to completely close off one port before opening another. That is caused by the introduction of a plenum as the means for isolating a bypass leakage port. The plenum requires a leak-proof seal between the valve and the valve housing. If the seal is not complete, and that seal must be maintained throughout the entire movement of the valve, it is likely that "dirty" gas will be exhausted directly. A second related problem is that the moving portion of the Houston valve is a single, unitary piece. Given the significant pressures to be overcome at one or more of the ports, it may be that failure to isolate one port may cause a failure to isolate all ports. Finally, given the complexity of the several Houston valve designs presented, it is reasonably likely that mixing of air and the dirty gases will occur such that substantially complete combustion will not occur.
Given the continuing drive to minimize the emission of hazardous fluids, it is necessary to restrict substantially completely the output of such fluids prior to incineration. In that regard, it is to be noted that the removal of hazardous components from exhausted fluids has been substantially raised, increasing from 90% removal to 95% removal to 99% and higher removal. Presently, removal of approximately 99.9% of contaminants from exhaust fluid is virtually a requirement. Therefore, it is essential that any valving mechanism for the control of hazardous-fluid flow be substantially completed sealed and that it permit no direct flow through of contaminated fluid to an exhaust stack.
Therefore, what is needed is a multi-port valve to be used in a regenerative incinerator that is relatively simple and that substantially eliminates the possibility of direct flow through of hazardous fluid to an exhaust stack. What is also needed is such a valve that does not require continuous sealing during any switching of fluid flow direction in order to remain effective. Further, what is needed is such a valve having components operable in a coordinated manner so as to ensure efficient and rapid switching of the flow of hazardous fluids through a combustion chamber with little or no bypass leakage.